Estimated Errors in |Vcd|/|Vcs| from Semileptonic D Decays

We estimate statistical and systematic errors in the extraction of the CKM ratio |Vcd|/|Vcs| from exclusive D-meson semileptonic decays using lattice QCD and anticipated new experimental results.Comment: LATTICE98(heavyqk), LaTeX, 3 pages, 2 postscript figures, uses espcrc2.sty and hyperbasics.te

The anti-B --> D* lepton anti-neutrino form factor at zero recoil and the determination of V(cb)

We summarize our lattice QCD study of the form factor at zero recoil in the decay anti-B --> D* lepton anti-neutrino. After careful consideration of all sources of systematic uncertainty, we find, h_A1(1) = 0.913(+0.024-0.017)(+0.017-0.030), where the first uncertainty is from statistics and fitting while the second combined uncertainty is from all other systematic effects.Comment: Lattice2001(HeavyQuark); 3 pages, 2 eps figures, espcrc2.st

B -> D l nu form factors and the determination of |Vcb|

The zero recoil limit of the B -> D l nu form factors is calculated on the lattice, which provides a model-independent determination of |Vcb|. Considering a ratio of form factors, in which the bulk of statistical and systematic errors cancel, we obtain a precise result both for h_+(1) and for h_-(1).Comment: LATTICE98(heavyqk), LaTeX, 3 pages, 3 postscript figures, uses espcrc2.st

The B -> D* l nu Form Factor at Zero Recoil

We describe a model independent lattice QCD method for determining the deviation from unity for h_{A1}(1), the B -> D* l nu form factor at zero recoil. We extend the double ratio method previously used to determine the B -> D l nu form factor. The bulk of statistical and systematic errors cancel in the double ratios we consider, yielding form factors which promise to reduce present theoretical uncertainties in the determination of V_{cb}. We present results from a prototype calculation at a single lattice spacing corresponding to beta=5.7.Comment: Lattice99(heavyquarks); 3 pgs, LaTe

Normal State O 17 NMR Studies of Sr2RuO4 under Uniaxial Stress

The effects of uniaxial compressive stress on the normal state O17 nuclear-magnetic-resonance properties of the unconventional superconductor Sr2RuO4 are reported. The paramagnetic shifts of both planar and apical oxygen sites show pronounced anomalies near the nominal a-axis strain μaaμv that maximizes the superconducting transition temperature Tc. The spin susceptibility weakly increases on lowering the temperature below T≃10 K, consistent with an enhanced density of states associated with passing the Fermi energy through a van Hove singularity. Although such a Lifshitz transition occurs in the γ band formed by the Ru dxy states hybridized with in-plane O pπ orbitals, the large Hund's coupling renormalizes the uniform spin susceptibility, which, in turn, affects the hyperfine fields of all nuclei. We estimate this "Stoner" renormalization S by combining the data with first-principles calculations and conclude that this is an important part of the strain effect, with implications for superconductivity. © 2019 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI

Discrete Nonholonomic Lagrangian Systems on Lie Groupoids

This paper studies the construction of geometric integrators for nonholonomic systems. We derive the nonholonomic discrete Euler-Lagrange equations in a setting which permits to deduce geometric integrators for continuous nonholonomic systems (reduced or not). The formalism is given in terms of Lie groupoids, specifying a discrete Lagrangian and a constraint submanifold on it. Additionally, it is necessary to fix a vector subbundle of the Lie algebroid associated to the Lie groupoid. We also discuss the existence of nonholonomic evolution operators in terms of the discrete nonholonomic Legendre transformations and in terms of adequate decompositions of the prolongation of the Lie groupoid. The characterization of the reversibility of the evolution operator and the discrete nonholonomic momentum equation are also considered. Finally, we illustrate with several classical examples the wide range of application of the theory (the discrete nonholonomic constrained particle, the Suslov system, the Chaplygin sleigh, the Veselova system, the rolling ball on a rotating table and the two wheeled planar mobile robot).Comment: 45 page

Sporopollenin as an efficient green support for covalent immobilization of a lipase

Sporopollenin exine capsules (SECs), derived from the spores of Lycopodium clavatum, have been functionalised with 1,n-diamines and the resulting aminoalkyl microcapsules used to immobilize Candida antarctica lipase B (Cal B) via a glutaradehyde-based diimine covalent linker. The supported enzyme efficiently catalyzes the esterification of oleic acid with ethanol. Initial rates using the SEC-CalBs were comparable to the commercial enzyme Novozym 435, but displayed up to 20-fold higher specific activity. The supported enzymes could also be recycled and after four cycles displayed only a modest decrease in conversions. In a kinetic resolution the SEC-CalBs efficiently acetylated rac-1-phenylethanol, with conversions up to 37% after 5 hours and product enantiomeric excesses of >99%. Related to this, the dynamic resolution of rac-1-phenylethylamine, in the presence of Pd-BaSO₄ and ammonium formate, led to the acetylated amine with a 94% conversion and >99% ee

Upper critical field for underdoped high-T_c superconductors. Pseudogap and stripe--phase

We investigate the upper critical field in a stripe--phase and in the presence of a phenomenological pseudogap. Our results indicate that the formation of stripes affects the Landau orbits and results in an enhancement of $H_{c2}$. On the other hand, phenomenologically introduced pseudogap leads to a reduction of the upper critical field. This effect is of particular importance when the magnitude of the gap is of the order of the superconducting transition temperature. We have found that a suppression of the upper critical field takes place also for the gap that originates from the charge--density waves.Comment: 7 pages, 5 figure

Spin fluctuations in nearly magnetic metals from ab-initio dynamical spin susceptibility calculations:application to Pd and Cr95V5

We describe our theoretical formalism and computational scheme for making ab-initio calculations of the dynamic paramagnetic spin susceptibilities of metals and alloys at finite temperatures. Its basis is Time-Dependent Density Functional Theory within an electronic multiple scattering, imaginary time Green function formalism. Results receive a natural interpretation in terms of overdamped oscillator systems making them suitable for incorporation into spin fluctuation theories. For illustration we apply our method to the nearly ferromagnetic metal Pd and the nearly antiferromagnetic chromium alloy Cr95V5. We compare and contrast the spin dynamics of these two metals and in each case identify those fluctuations with relaxation times much longer than typical electronic `hopping times'Comment: 21 pages, 9 figures. To appear in Physical Review B (July 2000

The Dependence of the Superconducting Transition Temperature of Organic Molecular Crystals on Intrinsically Non-Magnetic Disorder: a Signature of either Unconventional Superconductivity or Novel Local Magnetic Moment Formation

We give a theoretical analysis of published experimental studies of the effects of impurities and disorder on the superconducting transition temperature, T_c, of the organic molecular crystals kappa-ET_2X and beta-ET_2X (where ET is bis(ethylenedithio)tetrathiafulvalene and X is an anion eg I_3). The Abrikosov-Gorkov (AG) formula describes the suppression of T_c both by magnetic impurities in singlet superconductors, including s-wave superconductors and by non-magnetic impurities in a non-s-wave superconductor. We show that various sources of disorder lead to the suppression of T_c as described by the AG formula. This is confirmed by the excellent fit to the data, the fact that these materials are in the clean limit and the excellent agreement between the value of the interlayer hopping integral, t_perp, calculated from this fit and the value of t_perp found from angular-dependant magnetoresistance and quantum oscillation experiments. If the disorder is, as seems most likely, non-magnetic then the pairing state cannot be s-wave. We show that the cooling rate dependence of the magnetisation is inconsistent with paramagnetic impurities. Triplet pairing is ruled out by several experiments. If the disorder is non-magnetic then this implies that l>=2, in which case Occam's razor suggests that d-wave pairing is realised. Given the proximity of these materials to an antiferromagnetic Mott transition, it is possible that the disorder leads to the formation of local magnetic moments via some novel mechanism. Thus we conclude that either kappa-ET_2X and beta-ET_2X are d-wave superconductors or else they display a novel mechanism for the formation of localised moments. We suggest systematic experiments to differentiate between these scenarios.Comment: 18 pages, 5 figure